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Green Chemistry
Question Paper 2
Level
Subject
Exam Board
Topic
Sub-Topic
Booklet
A Level
Chemistry
OCR
Green Chemistry
Question Paper 2
88 minutes
Time Allowed:
Score:
/73
Percentage:
/100
Grade Boundaries:
A*
>85%
A
777.5%
B
C
D
E
U
70%
62.5%
57.5%
45%
<45%
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1
The uses of catalysts have great economic and environmental importance. For example, catalysts
are used in ammonia production and in catalytic converters.
(a) Nitrogen and hydrogen react together in the production of ammonia, NH3.
N2(g) + 3H2(g)
2NH3(g)
ΔH = –92 kJ mol–1
The activation energy for the forward reaction, Ea, is +250 kJ mol–1.
(i)
Complete the enthalpy profile diagram for this reaction between nitrogen and hydrogen.
Include the
•
•
•
enthalpy
products
enthalpy change of reaction, ΔH
activation energy for the forward reaction, Ea.
N2(g) + 3H2(g)
progress of reaction
[3]
(ii)
What is the value of the enthalpy change of formation of ammonia?
answer = ............................................. kJ mol–1 [1]
(iii)
The reaction between nitrogen and hydrogen can be catalysed.
Suggest a possible value for the activation energy of the catalysed forward reaction.
answer = ............................................. kJ mol–1 [1]
(iv)
What is the value of the activation energy for the uncatalysed reverse reaction (the
decomposition of ammonia into nitrogen and hydrogen)?
answer = ............................................. kJ mol–1 [1]
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(b) In a catalytic converter, nitrogen monoxide reacts with carbon monoxide.
(i)
Write the equation for this reaction.
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(ii)
Outline the stages that allow nitrogen monoxide and carbon monoxide to react in a
catalytic converter.
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(c) Scientists monitor pollutant gases in the atmosphere.
(i)
State two modern analytical techniques that scientists can use to monitor environmental
pollution.
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(ii)
Explain why it is important to establish international cooperation to reduce pollution
levels.
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(d) In the stratosphere, nitrogen monoxide, NO, is linked with ozone depletion.
Complete the equations below that describe how NO contributes to ozone depletion.
step 1
NO + O3
........... + ...........
step 2
NO2 + ...........
NO + ...........
overall
........... + ...........
2O2
[3]
(e) Hess’ law can be used to calculate enthalpy changes of reaction.
The equation for the reaction that gives the enthalpy change of formation, ΔHf, of N2O(g) is as
follows.
N2(g) + ½O2(g)
(i)
N2O(g)
It is not possible to measure the enthalpy change of formation of N2O(g) directly.
Suggest why it is not possible.
...........................................................................................................................................
..................................................................................................................................... [1]
(ii)
The data below can be used to calculate the enthalpy change of formation, ΔHf , of
N2O(g).
reaction
enthalpy change of reaction
/ kJ mol–1
C(s) + N2O(g)
CO(g) + N2(g)
–193
C(s) + ½O2(g)
CO(g)
–111
Calculate ΔHf for N2O(g).
ΔHf = ........................................... kJ mol–1 [2]
[Total: 19]
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2
Methane and ethane are important fuels.
(a) Methane could be manufactured by the reaction between carbon dioxide and hydrogen.
CO2(g) + 4H2(g)
CH4(g) + 2H2O(g)
Using the table of bond enthalpies, calculate the enthalpy change of reaction for this
manufacture of methane.
bond
average bond enthalpy
/ kJ mol–1
C–H
+415
H–H
+436
C=O
+805
O–H
+464
enthalpy change of reaction = ............................................ kJ mol–1 [3]
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(b) Methane is a greenhouse gas. Scientists are concerned that the concentration of methane in
the atmosphere is slowly increasing.
(i)
Explain how atmospheric methane molecules can contribute to global warming.
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(ii)
One way that scientists hope to minimise global warming is by developing Carbon
Capture and Storage, CCS, techniques.
Describe two of these CCS techniques.
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(c) Ethane reacts with bromine in the presence of ultraviolet radiation to form many organic
products.
(i)
Two of these products are bromoethane and hydrogen bromide.
Describe the mechanism of the reaction between ethane and bromine that forms
bromoethane and hydrogen bromide.
Include in your answer
•
•
•
the type of bond fission that occurs
equations for each step of the reaction
the name of each step of the reaction.
Your answer needs to be clear and well organised using the correct terminology.
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(ii)
Give two reasons why there are many organic products of the reaction between bromine
and ethane.
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[Total: 16]
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3
Nitrogen monoxide is an atmospheric pollutant, formed inside car engines by the reaction between
nitrogen and oxygen.
N2(g) + O2(g)
2NO(g)
ΔH = +66 kJ mol–1
This reaction is endothermic.
(a) (i)
Explain the meaning of the term endothermic.
...........................................................................................................................................
...................................................................................................................................... [1]
(ii)
What is the value for the enthalpy change of formation of nitrogen monoxide?
answer = ........................................... kJ mol–1 [1]
(b) (i)
Complete the enthalpy profile diagram for the reaction between nitrogen and oxygen.
On your diagram
•
•
•
add the product
label the activation energy as Ea
label the enthalpy change as ΔH.
enthalpy
N2(g) + O2(g)
reaction pathway
[3]
(ii)
Explain the meaning of the term activation energy.
...........................................................................................................................................
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...................................................................................................................................... [1]
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(c) A research chemist investigates the reaction between nitrogen and oxygen.
She mixes nitrogen and oxygen gases in a sealed container.
She then heats the container at a constant temperature for one day until the gases reach a
dynamic equilibrium.
(i)
Explain, in terms of the rate of the forward reaction and the rate of the backward reaction,
how the mixture of N2(g) and O2(g) reaches a dynamic equilibrium containing N2(g),
O2(g) and NO(g).
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(ii)
The research chemist repeats the experiment at the same temperature using the same
initial amounts of N2(g) and O2(g). This time she carries out the experiment at a much
higher pressure.
Suggest why
•
•
much less time is needed to reach dynamic equilibrium
the composition of the equilibrium mixture is the same as in the first experiment.
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(iii)
The reaction between nitrogen and oxygen in a car engine does not reach a dynamic
equilibrium.
Suggest why not.
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(d) Nitrogen monoxide is a radical.
What does this tell you about a molecule of nitrogen monoxide?
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(e) Oxides of nitrogen, NOx, are atmospheric pollutants.
(i)
Nitrogen monoxide reacts with oxygen to form NO2.
Write an equation for the formation of NO2 from nitrogen monoxide and oxygen.
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(ii)
Aeroplane engines produce nitrogen monoxide.
Describe, with the aid of equations, how nitrogen monoxide catalyses ozone depletion in
the stratosphere.
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(iii)
Outline the use of infrared spectroscopy in identifying air pollutants such as NOx.
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[Total: 21]
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4
Petrol and diesel are both complex mixtures of hydrocarbons used as fuels in transport.
(a) Petrol contains some branched chain alkanes.
The number of carbon atoms per molecule varies between five and nine.
Name one branched chain alkane with between five and nine carbon atoms.
.............................................................................................................................................. [1]
(b) When petrol burns in an internal combustion engine the exhaust gases contain CO2, CO, NO,
N2, O2, H2O and unburnt hydrocarbons.
(i)
What effect does the absorption of infrared radiation have on the bonds in CO2 molecules
in the atmosphere?
...................................................................................................................................... [1]
(ii)
Why is CO present in the exhaust gases?
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(iii)
Both NO and CO are atmospheric pollutants.
For each pollutant, describe one environmental problem.
NO ......................................................................................................................................
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CO ......................................................................................................................................
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(c) Most cars are fitted with a catalytic converter which catalyses the exothermic reaction between
NO and CO to form two less harmful gases.
(i)
Name the two gases formed and write an equation for this reaction.
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...................................................................................................................................... [2]
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(ii)
NO and CO react very slowly without a catalyst.
The catalyst in a catalytic converter increases the rate of reaction.
Explain, using an enthalpy profile diagram and the Boltzmann distribution model, how
the use of a catalyst increases the rate of reaction.
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(d) Many lorries and some cars use diesel powered engines.
Biodiesel is being developed as a substitute for diesel from crude oil.
Biodiesel is a methyl ester of a long chain carboxylic acid.
The flow chart shows how it is produced.
plants
plant oil
long chain carboxylic acids
biodiesel
Describe the benefits and disadvantages of changing from diesel to biodiesel.
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[Total: 17]